1. Field of the Invention
The present invention relates generally to spool-type hydraulic control valves and more particularly to valves which are automatically driven to a neutral position after a predetermined amount of pressure in excess of working pressure is reached.
2. Description of the Prior Art
Valves in this particular field of art have many uses, such as, for example, a hydraulic log splitter wherein it is desirable for an operator to temporarily be absent from the manual control while the valve is retracting in order to retrieve another work-piece or organize the split logs while the cylinder rod is retracting. The more common and least complex control valve presently used for hydraulic log-splitters has a spool which is spring-biased to the neutral position. If the valve is held against resistance when the cylinder is retracting, which occurs most often when the rod is fully retracted, a relief valve opens allowing the pressures in the working valves to be maintained at a present limit. The attitude of this valve is neutral unless the manual control is held in either of its two working positions.
A more complex valve presently used includes a detent for holding the spool in the retract position until a relief valve within an end of the valve's spool permits the application of fluid pressure great enough to overcome the detent and thereby return the valve to neutral. This valve permits the operator to leave the valve in the retract attitude while he is performing other tasks. However, in order for the detent to function satisfactorily pressures of a magnitude of 600 to 800 psi must be developed before the detent is overcome. While this valve generally has performed satisfactorily, pressures of this magnitude tend to shorten the life on the hydraulic pump and other components of the system. Furthermore, it includes an additional relief valve and the detent parts. Such a detent mechanism is costly to maintain and requires heat treated parts which must slide in and out of grooves under high pressure.
In addition, none of the prior art devices known to the inventor will automatically move into the retract position. Such a feature would be desirable in that the extra motion to so orient the manual control required by the more complex device described hereinabove is eliminated, and in operations where production is of consequence, it is unnecessary to train operators to place the manual control in retract in order that the cylinder will automatically return to an attitude for receipt of another work-piece prior to the operator removing his hand from the manual control lever.